Ultrasound trending and Vibration Analysis working together

This is a good example of how condition monitoring technologies work well as integrated technologies.

Through routine in house overall ultrasonic dB trending a change in condition was noted from one of the motor bearings and this was an increasing trend. I was called to verify the asset condition through vibration analysis.

Executive Summary:

Removal of the motor on condition of the bearing enabled a control change-out and a more cost efficient repair rather than running to failure.

The cause of the elevated Ultrasonic levels and the vibration defect frequencies was false Brinelling to the drive end bearing.

In addition there appears to be grease compatibility problems result from either mixing incompatible greases, or from ingress of other contaminate, Dry powers absorb the oil causing the grease to thicken.

Failure Mode:

From inspection the primary failure mode as per ISO 15243:2004 is 5.3.3.3 False Brinelling, there is also a secondary failure mode as per ISO 15243:2004 of 5.2.2 Abrasive Wear due to inadequate lubrication.

False Brinelling occurs in the contact area due to micromovements and/or resilience of the elastic contact under cyclic vibrations. Depending on the intensity of the vibrations, lubrication conditions and load, a combination of corrosion and wear can occur, forming shallow depressions in the raceway. In the case of a stationary bearing, the depressions appear at rolling element pitch.

In many cases, it is possible to discern rust at the bottom of the depressions. This is caused by oxidation of the detached particles, which have a large area in relation to their volume, as a result of their exposure to air.

Key Points are:

rolling element / raceway contact areas

micromovements / elastic deformation

vibrations

corrosion/wear shiny or reddish depressions

when stationary: at rolling element pitch

when rotating: parallel “flutes”

Abrasive wear. Most of the time, real abrasive wear occurs due to inadequate lubrication or the ingress of solid contaminants. Abrasive wear is generally characterised by dull surfaces. Abrasive wear is a degenerative process that eventually destroys the microgeometry of a bearing because wear particles further reduce the lubricant’s effectiveness. Abrasive particles can quickly wear down the raceways of rings and rolling elements, as well as cage pockets. Under poor lubrication conditions, the cage may be the first component to wear.

Image 2 is an image of the false Brinelling indetention on the inner raceway.

Image 2:

Image 3 is a microscopic image of a false Brinelling depression on the inner raceway. Rust at the bottom of the depressions. This is caused by oxidation of the detached particles

Image 3:

Image 4 is a microscopic image of the inner raceway showing the over roll of particles.

Image 4:

Image 5 is an image of the outer raceway in the load zone showing the false Brinelling. This is only present in the load zone.

Image 5:

Image 6 is a microscopic image of a false Brinelling depression on the outer raceway.

Image 6:

Image 7 is a microscopic image of a rolling element. Here you can see the flat spot from the false Brinelling. In addition the ring that is around the inner and outer raceway is due to over roll of particles and poor lubrication condition. Flat spot from the false Brinelling Ring of over roll of particles

Image 7:

Vibration Data:

The comparison below show Fan 1 (in blue) and Fan 2 (in green). This highlights the very high destructive levels of the drive end bearing and that it was close to failure.

The PeakVue spectrum plot below confirmed that it was a bearing defect and highest at the outer raceway.